Solid-state NMR spectroscopy, when combined with first-principles density functional theory (DFT) calculations, offers a highly sensitive probe of atomic-scale structure and dynamics in solid-state ion conductors, enabling the characterisation of subtle features that govern ionic conductivity. However, current approaches for interpreting NMR spectra rely on a comparison with static DFT reference calculations, which are inadequate for materials exhibiting fast ion dynamics such as lithium battery solid electrolytes. Here, using room-temperature NMR measurements and first-principles calculations, we show that the standard static-structure approach fails to reproduce the experimental 35Cl isotropic chemical shift (δ iso) of the fast Li-ion conductor Li6PS5Cl and substantially overestimates the quadrupolar coupling constant (C Q). We show that this discrepancy can be resolved using only ten DFT calculations by sampling relaxed configurations representative of Li-ion diffusion from machine-learning molecular dynamics. Compared with vibrational motion, Li-ion hopping around Cl is shown to dominate the motional averaging through reorientation of the NMR tensors. This study therefore provides an efficient computational method to resolve the complexities of the NMR spectra of Li6PS5Cl, which can be widely applied to other ion-conducting solids.

Rechargeable batteries represent a key transformative technology for electric vehicles, portable electronics, and renewable energy. Yet, there are few nondestructive diagnostic techniques compatible with realistic commercial cell enclosures. Many battery failures result from the loss or chemical degradation of the electrolyte. In this work, we present measurements through battery enclosures that allow quantification of electrolyte amount and composition. The study employs instrumentation and techniques developed in the context of zero-to-ultralow-field nuclear magnetic resonance (ZULF NMR), with quantum magnetometers as the detection elements (atomic optically pumped magnetometers, OPMs, and superconducting quantum interference devices, SQUIDs, used in this work). In contrast to conventional NMR methodology, which suffers from skin-depth limitations, the reduced resonance frequencies in ZULF NMR make battery housing and electrodes transparent to the electromagnetic fields involved. As demonstrated here through simulation and experiment, both the solvent and lithium-salt components of the electrolyte (lithium hexafluorophosphate, LiPF6) signature can be quantified using our techniques. Further, we show that the ZULF-NMR apparatus and technique are compatible with measurements of pouch-cell batteries.

The rate performance of all-solid-state batteries can be limited by the low conductivity of the solid electrolyte in the composite cathode. A conductivity of 10 mS cm-1 is required, which exceeds that of many solid electrolytes. This limitation can be attributed to intra- and inter-grain ion transport. Understanding the limitations of ion transport is a multi-length scale problem ranging from single bond hops to particle-particle transport. Here we show that spark plasma sintering of Li6PS5Cl not only enhances ion transport on the macroscopic length scale but also on the microscopic scale. On the macroscopic length scale, greater densification improves particle-to-particle contact. On the nanoscale, short-range order (SRO) of the neighbouring 4a/4a and 4d/4d Wyckoff sites present in the cold-pressed Li6PS5Cl produces unfavourable Li ion pathways through the cell. Spark plasma heating removes the SRO, creating a connected network of microscopic pathways for the Li to migrate. Finally, on the atomistic level, spark plasma heating increases the amount of Cl- residing on the 4d site and S2- on the 4a site. By understanding the limitations of ion mobility across a range of length scales, one can target methods to produce solid-state argyrodite electrolytes with higher ionic conductivities.

The lithium–air (oxygen) battery could offer significant improvements in gravimetric energy density compared to lithium-ion technology. 1 A major barrier to a practical device is the oxidative degradation of the electrolyte solution and the carbon at the positive electrode. 2 Recently, the lithium–oxygen field has been focused on the formation of singlet oxygen within the cell, its impact as a major source of degradation, and strategies to mitigate this. We have investigated the reactivity of components within the lithium–oxygen cell by exposure to photochemically generated singlet oxygen both with and without an oxidising potential. 3 This approach to screening electrolytes against singlet oxygen is described, where tetraglyme, lithium bis(trifluoromethanesulfonyl)imide, or carbon, standard lithium-oxygen cell components, are reviewed. The role singlet oxygen plays in degradation of the lithium–oxygen battery is discussed, as well as the perspective to refocus on the discovery of electrolyte solutions with stability against major antagonists. [1] Aurbach, D., McCloskey, B., Nazar, L. et al. Advances in understanding mechanisms underpinning lithium–air batteries., Nat. Energy., 1: 16128 ( 2016 ); [2] Jethwa, R. B., Mondal, S., Pant, B., Freunberger, S. A., To DISP or not? The Far-Reaching Reaction Mechanisms Underpinning Lithium-air batteries., Angew. Chem. Int. Ed., e202316476 ( 2023 ); [3] Zor, C, Jones, K. D., Rees, G. J., Yang, S., Pateman, A., Gao, X., Johnson, L. R., Bruce, P. G., Singlet oxygen is not the main source of electrolyte degradation in lithium oxygen batteries., Energy Environ. Sci .,17: 7355-7361 ( 2024 ) Figure 1

Enabling recycling and improving performance are key challenges for next‐generation electrolytes for rechargeable batteries. Here, an equilibrium polymerization: trimethylene carbonate (TMC) ring‐opening polymerization, in the presence of lithium difluoro(oxalato)borate salt, is utilized to form an electrolyte in situ during coin cell fabrication for lithium batteries. This process creates a semi‐solid poly(trimethylene carbonate) electrolyte with high ambient ionic conductivity (0.52 mS cm −1 ), thermal stability ( T d, 5% = 160 °C), and oxidative stability up to 4.7 V. Using this electrolyte with commercial lithium iron phosphate cathodes, results in 97% capacity retention after 350 cycles at 2C, achieving theoretical capacities of 170 mAh g −1 at 0.1C. The cells retain excellent performance at high current densities (86 mAh g −1 at 4C). Post‐use, the polymer can be separated from the salt and selectively recycled to pure starting monomer (TMC) through a solid‐state chemical recycling process. The recycled monomer, when repolymerized to reform the polycarbonate electrolyte, yields cells with performance identical to the original. The exploitation of polymerization‐depolymerization equilibria offers a useful strategy for enhancing battery performance, ensuring effective material recycling, and advancing a circular economy.

In this paper, we report the synthesis of Li2OHX (X = Br, Cl)-based glasses. These glasses were found to be challenging to synthesize, requiring extreme cooling rates achievable only by a twin-roll quench process. As has been speculated for antiperovskite-derived glasses, indications of improved lithium-ion dynamics are observed. Notably, spin-lattice relaxation nuclear magnetic resonance spectroscopy reveals a higher hopping frequency and significantly lower activation energy for Li2OHBr glasses (0.29 eV) compared to the crystalline Li2OHBr (0.39 eV). This may be attributable to the increased free volume in the glass samples (rho glass/rho cryst = 0.83) and a reduced ionic interaction of lithium ions with the glass structure. Despite these promising findings, the glasses were found to be unstable under pressure and crystallized in attempts to produce bulk samples for impedance measurements.

Disordered rocksalt cathodes deliver high energy densities, but they suffer from pronounced capacity and voltage fade on cycling. Here, we investigate fade using two disordered rocksalt lithium manganese oxyfluorides: Li3Mn2O3F2 (Li1.2Mn0.8O1.2F0.8), which stores charge by Mn2+/Mn4+ redox, and Li2MnO2F, where charge storage involves both Mn3+/Mn4+ and oxygen redox (O-redox). Li3Mn2O3F2 is reported for the first time. We identify the growth of an electronically resistive surface layer with cycling that is present in both Li2MnO2F and Li3Mn2O3F2 but more pronounced in the presence of O-redox. This resistive surface inhibits electronic contact between particles, leading to the observed voltage polarization and capacity loss. By increasing carbon loading in the composite cathode, it is possible to substantially improve the cycling performance. These results help to disentangle O-redox from other leading causes of capacity fading in Mn oxyfluorides and highlight the importance of maintaining electronic conductivity in improving capacity and voltage retention.

Avoiding lithium dendrites at the lithium/ceramic electrolyte interface and as a result avoiding cell short-circuit when plating at practical current densities remains a significant challenge for all-solid-state batteries. Typically, values are limited to around 1 mA cm-2, even, for example, for garnets with a relative density of >99%. It is not obvious that simply densifying ceramic electrolytes will deliver high plating currents. Here we show that plating currents of 9 mA cm-2 can be achieved without dendrite formation, by densifying Argyrodite, Li6PS5Cl, to 99%. Changes in the microstructure of Li6PS5Cl on densification from 83 to 99% were determined by FIB-SEM tomography and used to calculate their effect on the critical current density (CCD). Not all changes in microstructure with densification act to increase CCD. While smaller pores and shorter cracks increase CCD, lower pore population and narrower cracks act to decrease CCD. Calculations show that the former changes dominate over the latter, predicating an overall increase in CCD, as observed experimentally.

Electrolyte degradation in Li–O 2 batteries arises from reactions with growing Li 2 O 2 surfaces, not superoxide or singlet oxygen, directing future research toward stable solvent design.

The fluoride-ion battery (FIB) is a post-lithium anionic battery that utilizes the fluoride-ion shuttle, achieving high theoretical energy densities of up to 1393 Wh L-1 without relying on critical minerals. However, developing liquid electrolytes for FIBs has proven arduous due to the low solubility of fluoride salts and the chemical reactivity of the fluoride ion. By introducing a chemically stable electrolyte based on 1,3-dimethylimidazolium [MMIm] bis(trifluoromethanesulfonyl)imide [TFSI] and tetramethylammonium fluoride (TMAF), we achieve an electrochemical stability window (ESW) of 4.65 V, ionic conductivity of 9.53 mS cm -1, and a solubility of 0.67 m. The origin of this high solubility and the solvation structure were investigated using NMR spectroscopy and neutron total scattering, showing a fluoride solvation driven by strong electrostatic interactions and weak hydrogen bonding without covalent H-F character. This indicates the chemical stability of 1,3-dimethylimidazolium toward the fluoride ion and its potential as an electrolyte for high-voltage FIBs.

The very high theoretical specific energy of the lithium-air (Li-O2) battery (3500 Wh kg-1) compared with other batteries makes it potentially attractive, especially for the electrification of flight. While progress has been made in realizing the Li-air battery, several challenges remain. One such challenge is achieving a high capacity to store charge at the positive electrode at practical current densities, without which Li-air batteries will not outperform lithium-ion. The capacity is limited by the mass transport of O2 throughout the porous carbon positive electrode. Here it is shown that by replacing the binder in the electrode by a polymer with the intrinsic ability to transport O2, it is possible to reach capacities as high as 31 mAh cm-2 at 1 mA cm-2 in a 300 µm thick electrode. This corresponds to a positive electrode energy density of 2650 Wh L-1 and specific energy of 1716 Wh kg-1, exceeding significantly Li-ion batteries and previously reported Li-O2 cells. Due to the enhanced oxygen diffusion imparted by the gas diffusion polymer, Li2O2 (the product of O2 reduction on discharge) fills a greater volume fraction of the electrode and is more homogeneously distributed.

LiNiO2 remains a critical archetypal material for high energy density Li-ion batteries, forming the basis of Ni-rich cathodes in use today. Nevertheless, there are still uncertainties surrounding the charging mechanism at high states of charge and the potential role of oxygen redox. We show that oxidation of O2- across the 4.2 V plateau forms O2 trapped in the particles and is accompanied by the formation of 8% Ni vacancies on the transition metal sites of previously fully dense transition metal layers. Such Ni vacancy formation on charging activates O-redox by generating non-bonding O 2p orbitals and is necessary to form vacancy clusters to accommodate O2 in the particles. Ni accumulates at and near the surface of the particles on charging, forming a Ni-rich shell approximately 5 nm thick, enhanced by loss of O2 from the surface, the resulting shell composition is Ni2.3+1.75O2. The overall Ni oxidation state of the particles measured by XAS in fluorescence yield mode after charging across the plateau to 4.3 V is approximately +3.8; however, taking account of the shell thickness and the shell Ni oxidation state of +2.3, this indicates a Ni oxidation state in the core closer to +4 for compositions beyond the plateau.

Improving composite cathode function is key to the success of the solid-state battery. Maximizing attainable cathode capacity and retention requires integrating suitable polymeric binders that retain a sufficiently high ionic conductivity and long-term chemo-mechanical stability of the cathode active material-solid-electrolyte-carbon mixture. Herein, we report block copolymer networks composed of lithium borate polycarbonates and poly(ethylene oxide) that improved the capacity (200 mAh g −1 at 1.75 mA cm −2 ) and capacity retention (94 % over 300 cycles) of all-solid-state composite cathodes with nickel-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode active material, Li 6 PS 5 Cl solid electrolyte, and carbon. Tetrahedral B(OR) 2 (OH) 2 − anions immobilized on the polycarbonate segments provide hydrogen-bonding chain crosslinking and selective Li-counterion conductivity, parameterized by Li-ion transference numbers close to unity ( t Li+ ~0.94). With 90 wt % polycarbonate content and a flexible low glass transition temperature backbone, the single-ion conductors achieved high Li-ion conductivities of 0.2 mS cm −1 at 30 °C. The work should inform future binder design for improving the processability of cathode composites towards commercializing solid-state batteries, and allow use in other cell configurations, such as lithium-sulphur cathode designs.

Charging current densities of solid-state batteries with lithium metal anodes and ceramic electrolytes are severely limited due to lithium dendrites that penetrate the electrolyte leading to a short circuit. We show that dendrite growth can be inhibited by different crack deflection mechanisms when multi-layered solid electrolytes, such as Li6PS5Cl/Li3ScCl6/Li6PS5Cl and Li6PS5Cl/Li10GeP2S12/Li6PS5Cl, are employed but not when the inner layer is Li3PS4. X-ray tomographic imaging shows crack deflection along mechanically weak interfaces between solid electrolytes as a result of local mismatches in elastic moduli. Cracks are also deflected laterally within Li3ScCl6, which contains preferentially oriented particles. Deflection occurs without lithium being present. In cases where the inner layers react with lithium, the resulting decomposition products can fill and block crack propagation. All three mechanisms are effective at low stack pressures. Operating at 2.5 MPa, multi-layered solid electrolytes Li6PS5Cl/Li3ScCl6/Li6PS5Cl and Li6PS5Cl/Li10GeP2S12/Li6PS5Cl can achieve lithium plating at current densities exceeding 15 mA cm−2.

Although reliable rechargeable batteries represent a key transformative technology for electric vehicles, portable electronics, and renewable energy, there are few nondestructive diagnostic techniques compatible with realistic commercial cell enclosures. Many battery failures result from the loss or chemical degradation of electrolyte. In this work, we present measurements through battery enclosures that allow quantification of electrolyte amount and composition. The study employs instrumentation and techniques developed in the context of zero-to-ultralow-field nuclear magnetic resonance (ZULF NMR), with optical atomic magnetometers as the detection elements. In contrast to conventional NMR methodology, which suffers from skin-depth limitations, the reduced resonance frequencies in ZULF NMR make battery housing and electrodes transparent to the electromagnetic fields involved. As demonstrated here through simulation and experiment, both the solvent and lithium-salt components of the electrolyte (LiPF6) signature could be quantified using our techniques. Further, we show that the apparatus is compatible with measurement of pouch-cell batteries.

A series of poly(ester- b -carbonate) electrolytes are prepared by a one-pot procedure and structure–property relationships are observed. The polymer was used as a composite cathode binder with excellent discharge capacity and capacity retention.

Oxygen redox cathodes, such as Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , deliver higher energy densities than those based on transition metal redox alone. However, they commonly exhibit voltage fade, a gradually diminishing discharge voltage on extended cycling. Recent research has shown that, on the first charge, oxidation of O 2− ions forms O 2 molecules trapped in nano-sized voids within the structure, which can be fully reduced to O 2− on the subsequent discharge. Here we show that the loss of O-redox capacity on cycling and therefore voltage fade arises from a combination of a reduction in the reversibility of the O 2− /O 2 redox process and O 2 loss. The closed voids that trap O 2 grow on cycling, rendering more of the trapped O 2 electrochemically inactive. The size and density of voids leads to cracking of the particles and open voids at the surfaces, releasing O 2 . Our findings implicate the thermodynamic driving force to form O 2 as the root cause of transition metal migration, void formation and consequently voltage fade in Li-rich cathodes.

The cathode-electrolyte interphase (CEI) in Li-ion batteries plays a key role in suppressing undesired side-reactions whilst facilitating Li-ion transport. Ni-rich layered cathode materials offer improved energy densities, but their high interfacial reactivities can negatively impact cycle life and rate performance. Here we investigate the role of electrolyte salt concentration, specifically LiPF6 (0.5-5 m), in altering the interfacial reactivity of charged LiN0.8Mn0.1Co0.1O2 (NMC811) cathodes in standard carbonate based electrolytes (EC:EMC vol%:vol% 3:7). Extended potential holds of NMC811/Li4Ti5O12 (LTO) cells reveal that the parasitic electrolyte oxidation currents observed are strongly dependent on the electrolyte salt concentration. X-ray photoelectron and absorption spectroscopy (XPS/XAS) reveal that a thicker LixPOyFz-/LiF-rich CEI is formed in the more highly concentrated electrolytes. This suppresses reactions with solvent molecules resulting in a thinner, or less-dense, reduced surface layer (RSL) with lower charge transfer resistance, and lower oxidation currents at high potentials. The thicker CEI also limits access of acidic species to the RSL suppressing transition metal dissolution into the electrolyte, as confirmed by nuclear magnetic resonance (NMR) spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES). This provides insight into the main degradation processes occurring at Ni-rich cathode interfaces in contact with carbonate based electrolytes, and how electrolyte formulation can help to mitigate these.

The lithium-air (oxygen) battery could offer significant improvements in gravimetric energy density compared to lithium-ion technology. A major barrier to realising this goal is the oxidative degradation of the electrolyte...

Solid-state electrolytes (SEs) hold the potential to overcome challenges that hinder the commercialization of lithium-sulfur batteries. However, their limited ionic conductivity makes lithium (Li) ion transport a critical bottleneck in accessing the superior capacity of sulfur. In this study, we investigate high-entropy Cl,Br-co-doped sulfide argyrodites as SEs in Li-sulfur (S) all-solid-state batteries (ASSBs). Li 5.7 PS 4.7 Cl 0.65 Br 0.65 exhibits an ionic conductivity of 6.9 mS cm- 1 at room temperature with an activation energy of 0.28 eV, thanks to its high configurational entropy. The electrolyte with suitable cathodic stability and high ionic conductivity allows S composite cathodes to deliver an areal capacity over 6 mAh cm- 2 when cycled with Li-In anodes. The reduced porosity of the SE separator and the formation of a passivating interphase with metallic Li enable Li-S ASSBs to cycle without short circuits, achieving an S utilization of over 75% at 0.1 C.